In this study of the longitudinal course of the development of mastery motivations, the goals are to determine whether mastery motivation in infancy is predictive of later mastery behavior and whether specific aspects of parent-infant interaction influence mastery behavior at 2 1/2 years. The interrelationships between the development of cognitive functions and mastery motivation during the preschool years is also being studied. Methods have been developed to assess similar aspects of mastery at 2 1/2 years as were studied at 6 and 12 months of age. Data are being collected using these measures of mastery in a focused play session, an observation of the infant's free play with the mastery toys, and a brief observation of mother-child interaction with another set of toys. Data on cognitive development are being obtained by the use of the McCarthy scales.